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February 14, 2013

Extinction May Be Greater Engine For Plant Biodiversity Than Evolution

by Peter Suciu for redOrbit.com – Your Universe Online

Peter Suciu for redOrbit.com — Your Universe Online

German philosopher Friedrich Nietzsche famously said “that which does kill us makes us stronger,” but apparently he didn´t understand the complexities of biodiversity. If he had, he might have noted that extinction could influence biodiversity as much as evolution.

This is what researchers at the University of Melbourne and the University of Tasmania have discovered while examining plant diversity in South East Australia. Their findings suggest that Australia´s rich plant diversity was likely wiped out during the ice ages, probably around one million years ago.

“Traditionally scientists believed some places have more species than others because species evolved more rapidly in these places,” said Dr. Kale Sniderman of the University of Melbourne, School of Earth Sciences. “We have overthrown this theory, which emphasizes evolution, by showing that extinction may be more important.”

Sniderman´s line of research has included the reconstruction of Early Pleistocene climate in southern Australia and its implications for Southern Hemisphere atmospheric circulation. His most recent study, which was conducted in collaboration with the Nelson Mandela Metropolitan University in South Africa, compares two regions in Southern Australia and South Africa.

In this study he noted that southwestern Australia has an enormous diversity of tough-leaved shrubs and trees such as eucalypts, Banksia, Grevilleas and Acacias. However, Sniderman found that the southern tip of South Africa is even richer, and is home to a number of similar plants such as Proteas and Ericas. Past studies have suggested that this diversity might somehow be related to the poor soils and dry summers in these distant regions.

For the recent study Sniderman´s team analyzed plant fossils that accumulated in an ancient lake in South Eastern Australia, and there they found that the region had at least as many tough-leaved plants 1.5 million years ago as Western Australia and South Africa do today — results the researchers say were unexpected.

Sniderman explained that current research suggests that as Australia dried out over the past several millions years as rainforest plants largely disappeared from most of the continent. This drying trend was thus thought to have allowed Australia´s characteristically tough-leaved plants to expand and become all the more diverse.

“We have shown that the climate variability of the ice ages not only drove rainforest plants to extinction but also a remarkable number of tough-leaved, shrubby plants,” Sniderman added.

This research has also convinced other scientists to reexamine their views on the biodiversity of Australia. This included Dr. Greg Jordan of the School of Plant Sciences at the University of Tasmania, who has primarily focused on the evolution of Australia´s vegetation, particularly Tasmania´s unique flora.

Jordan noted that Sniderman´s study has overturned current thought on the role of extinction in plant diversity, and that this could have implications for our understanding of how plant diversity is affected by past, present and future climate change.

“The species that went extinct in SE Australia during the ice ages were likely to be the ones most sensitive to rapid climate change, meaning that the species that now grow in eastern Australia may be more capable of tolerating rapid changes than predicted by current science,” explained Jordan. “However, the species in hotspots of diversity like Western Australia may be much more sensitive to future climate change, because they have been protected from past climate changes.”